Second TV screen. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Телевидение
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Owners of obsolete domestically produced computers often sell them literally for next to nothing, either as a set or in parts. There are many such facts. Meanwhile, these products can be usefully used by radio amateurs. In this regard, a black-and-white monitor is interesting, on the basis of which you can build a set-top box that duplicates, for example, in the kitchen, the image of a TV set installed in the living room.
The proposed attachment (Fig. 1) is designed to work together with the MS-6105.01 monitor. Unfortunately, it does not have its own power supply. Therefore, when developing the set-top box, it was necessary to assemble such a unit containing a T1 step-down transformer, a VD1-VD4 diode rectifier, a voltage regulator on a DA1 chip and a VT3 transistor.
The second important node of the set-top box is the 3H amplifier on the DA2 chip. and the third is a two-stage video amplifier based on transistors VT1, VT2. Plugs XP2, XP3 are connected to a source of video and audio signals (for example, a VCR), and to sockets XS1, XS2 - a consumer (say, a TV). In this case, the video signal enters through the capacitor C1 and the resistor R1 to the first stage of the video amplifier. Due to the high input impedance, it has almost no effect on the video signal level at the source output.
From the output of the first stage, the video signal is fed through a coaxial cable to the second stage, and from its output to the monitor. The set-top box is connected to it using the XP4 connector. The video signal level is regulated by a trimming resistor R9.
The audio signal through the resistor R3 and the shielded wire is fed to the variable resistor R7 (volume control), and from its slider to the 3H amplifier. The output signal of the amplifier through the capacitor C8 and pin 2 of the XP4 connector goes to the dynamic head (its outputs are connected to pin 2 and a common wire) installed inside the monitor.
Instead of the transistor VT1, it is permissible to use any other of the KT312, KT315, KT316, KTZ102 series, and instead of VT2 - any of the KT361, KT3107 series. As VT3, any of the series indicated in the diagram is suitable. Rectifier diodes can be any, allowing a current of at least 2 A. LED HL1 (indicator of the inclusion of the set-top box) - any small-sized. Oxide capacitors C1-C8 - series K50, C9 - K10-17. K73. Variable resistor R7 - SP-1, trimmer R9 - SPZ-3. SPZ-19. permanent - MLT. C2-33. Sockets XS1. XS2 and XP2, XP3 plugs - "tulip" type, XP4 connector - five-pin, mating part of the monitor connector (its pin 5 must be connected to jumper 346 on the monitor board). Any ready-made transformer is applicable, providing a voltage of 15 ... 17 V on the winding II at a load current of up to 3 A.
The sockets, parts of the first stage of the video amplifier and the resistor R3 are placed in a separate case and mounted using the surface mounting method. The case is placed near a VCR or TV. Most of the other parts are mounted on a printed circuit board (Fig. 2) made of one-sided foil material. Both microcircuits and the VT3 transistor are supplied with heat sinks.
Establishing a set-top box comes down to setting the required video signal level with a tuned resistor.
If you manage to use a monitor with a built-in or included power supply (these are monitors MS-6105.05 - MS-6105.08). the design of the set-top box will be simplified - the 3H amplifier and the video amplifier are powered by this unit, and all parts are placed in the monitor case.
This set-top box can also be used with a VCR tuner or for watching videos.
Author: I. Nechaev, Kursk
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